1. Field of the Invention
The present invention relates to a novel method for producing 1,2-benzisothiazol-3-ones, using 2-(alkylthio)benzaldehydes or 2-(alkylthio)benzaldehyde oximes as starting materials. The present invention also relates to a novel method for producing 2-(alkylthio)benzonitriles using 2-halobenzonitriles as starting materials, and to a novel method for producing 1,2-benzisothiazol-3-ones from the 2-(alkylthio)benzonitriles obtained by the method of the present invention. 1,2-benzisothiazol-3-ones are compounds useful as antibacterial agents and antifungal agents.
2. Discussion of the Related Art
The following methods are known for producing 1,2-benzisothiazol-3-ones.
(A) Bull. Chem. Soc. Jpn., 55, 1183-1187 (1982)
In this method, 2-(methylthio)benzamide is produced from 2-(methylthio)benzoyl chloride; oxidized with periodic acid to 2-(methylsulfinyl)benzamide; and cyclized in the presence of thionyl chloride to yield a 1,2-benzisothiazol-3-one. ##STR1## (B) Org. Prep. Proced. Int., 15, 315-319(1983)
In this method, a 1,2-benzisothiazol-3-one is obtained in 4 steps, using thiosalicylic acid as a starting material. ##STR2## (C) Ger. Offen. 3500577 (1986)
In this method, a desired 1,2-benzisothiazol-3-one is obtained using thiosalicylic acid as a starting material and sodium hydroxide in the final cyclization process. ##STR3##
The present applicant have filed patent applications for the following methods as modified methods of the above known methods.
(D) Japanese Patent Application No. 5-350932 titled "A method for producing 1,2-benzisothiazol-3-ones" filed on Dec. 29, 1993. ##STR4## (E) Japanese Patent Application No. 6-151476 titled "A method for producing isothiazolone derivatives" filed on Jun. 8, 1994. ##STR5##
However, the above known conventional methods have the following drawbacks:
In Method (A), the starting 2-(methylthio)benzoyl chloride has problems of high production cost and poor stability. This method also requires the use of an expensive periodic acid which is dangerous in handling and involves many reaction steps.
Methods (B) and (C) require the use of expensive thiosalicylic acid as the starting material and involve many reaction steps. Therefore, this method is not satisfactory for industrial use.
Methods (D) and (E) proposed by the present applicant are modifications of the above conventional methods, where a starting 2-(alkylthio)benzamide reacts with a halogenating agent.
As stated above, all known methods are not satisfactory for production on an industrial scale.